International Concrete Abstracts Portal

The deformability of reinforced concrete walls with staggered lap splices was studied through tests of six cantilevered walls under constant axial load and cyclic reversals of lateral displacement. The height-to-length aspect ratios of the walls were approximately 3.2. Four walls had staggered laps, one wall had non-staggered laps, and one wall had mechanical couplers. Laps were detailed to yield the spliced reinforcement. Test walls with staggered laps lost lateral-load resistance at smaller drift ratios (1.0% to 2.1%) than both the test wall with non-staggered laps (2.3%) and the test wall with mechanical couplers (3.5%). Staggered lap splices resulted in larger strain concentrations than non-staggered lap splices. It was concluded that both staggered and non-staggered lap splices a) can have reduced strain capacity relative to continuous bars (leading to bond failure before or after yield) and b) alter inelastic strain distributions, causing large reductions in effective plastic hinge length.

It can be demonstrated that performance-based seismic design of post-installed anchors in accordance with ACI 318 is not possible by using the anchor qualification information provided by ACI 355. The current state-of-the-art anchor qualification does not provide capacities that reflect actual earthquake responses in seismic design scenarios. This paper provides a comprehensive analysis and highlights the gaps in the current approach. A performance-based framework is proposed as the basis of future developments in seismic design and qualification of post-installed anchors. It is demonstrated that the approach is fully transparent and provides the possibility to identify key driving parameters that need further experimental investigation. The approach acknowledges that performance-based seismic design of post-installed anchors needs an understanding of the seismic damage of the concrete-anchor system. Currently, no design tools are available to predict this damage. The proposed framework adopts the theory of the accumulated damage potential (ADP) as a damage parameter. It is demonstrated that the selected damage parameter is simple but meaningful enough to represent the seismic damage of the concrete-anchor system at the design level. Possibilities for future development of the approach is explored, and directions for the next steps are suggested. It is highlighted that a definition of a framework for realistic seismic performance objectives of post-installed anchors is needed for the development of design tools in the future. The proposed framework has great practical significance and may help fill a gap in the seismic design of post-installed anchors. Promoting a transparent framework that is driven by the needs of performance-based seismic design may help develop a feasible qualification system and replace the currently used pass-or-fail assessment approach that is not suitable to provide anchor capacities for performance-based seismic design.

The paper presents a comparative study on the seismic behavior of circular columns reinforced with glass fiber-reinforced polymer (GFRP) and steel. The study specifically investigates the influence of replacing steel bars with GFRP bars on columns’ seismic response. All the studies summarized in this article were conducted at the University of Toronto. Results from the tests of 24 columns (all having 356 mm diameter and tested in a similar manner) from three different studies are closely analyzed to compare their responses. Based on the experimental results, it is found that replacing steel spirals with GFRP spirals did not result in substantial variation in the seismic performance of columns. Both types demonstrated similar ductility parameters and drift ratios when similar amounts of spirals were used at comparable pitches. Likewise, columns with steel longitudinal reinforcement and GFRP longitudinal reinforcement achieved similar displacement ductility, energy dissipation, and drift ratio.

In performance-based seismic design, buckling and fracture of longitudinal steel in reinforced concrete columns are damage limit states that may be considered for damage control and near collapse, respectively. This study evaluates the progression of buckling instability, which eventually leads to bar fracture, based on bending strains measured in buckled bars of cyclic quasi-static column tests. Buckling-induced bending strains are calculated with bare bar fiber models and experimental buckled shapes of longitudinal reinforcement in the column data set. This study proposes an empirical equation that calculates the buckling-induced bending strain based on column displacement ductility, low-cycle fatigue, and column design parameters for grade 60 steel. This study also identifies the buckling-induced bending strains that trigger transverse steel yielding, visual bar buckling, and brittle bar fracture.

Previous research studies have been conducted to study the seismic response of low-aspect-ratio RC shear walls when designed using normal-strength reinforcement (NSR) versus high-strength reinforcement (HSR). Such studies demonstrated that the use of HSR has the potential to address several constructability issues in nuclear construction practice by reducing the required steel areas and subsequently rebar congestion. However, the response of nuclear RC shear walls (i.e., aspect ratios of less than one) with both HSR and axial loads has not yet been evaluated under ground motion sequences. As such, most nuclear design standards restrict the use of HSR in nuclear RC shear wall systems. Such design standards do not consider the influence of axial loads when the shear strength capacity of such walls is calculated. To address this gap, the current study investigates the influence of axial load on the performance of nuclear RC shear walls with HSR when subjected to ground motion sequences using hybrid simulation testing and modelling assessment techniques. In this respect, two RC shear walls (i.e., W1-HSR and W2-HSR-AL), with an aspect ratio of 0.83, are investigated. Wall W2-HSR-AL had an axial load of 3.5% of its axial compressive strength, while wall W1-HSR had no axial load. The test walls were subjected to a wide range of ground motion records, from operational basis earthquake (OBE) to beyond design basis earthquake (BDBE) levels. The experimental results of the walls are discussed in terms of their damage sequences, cracking patterns, ductility capacities, effective periods, and rebar strains. The test results are then used to develop and validate a numerical OpenSees model that simulates the seismic response of nuclear RC shear walls with different axial load levels. Finally, the experimental and numerical results are compared to the current ASCE 41-23 backbone model for RC shear walls. The experimental results demonstrate that walls W1-HSR and W2-HSR-AL showed similar crack patterns and subsequent shear-flexure failures; however, the former had wider cracks relative to the former during the different ground motion records. In addition, the axial load reduced the displacement ductility of wall W2-HSR-AL by 18% compared to wall W1-HSR. Moreover, the ASCE 41-23 backbone model was not able to adequately capture the seismic response of the two test walls. The current study enlarges the experimental and numerical/analytical database pertaining to the seismic performance of low-aspect-ratio RC shear walls with HSR to facilitate their adoption in nuclear construction practice.